Basics
                   
Haskell is an example of a functional programming language. Some features of a functional language are:

   1. No variables
   2. Program = a list of function, type, and constant declarations
   3. Functions can be called or treated like data
   
A good reference on Haskell is:

   "Haskell: The Craft of Functional Programming" 
   by Simon Thompson
   Addison-Wesley 1996.
   
Of course there are plenty of tutorials avaialable on the web.

Gofer is a free PC implementation of a Haskell-like language. Hugs is a free PC implementation of a subset of Haskell. Students should download and install Hugs. In these notes all subsequent references to Haskell will actually be references to Hugs.

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Here is a complete list of the meta commands understood by the Hugs interpreter:

:load <filenames> load modules from specified files
:load               clear all files except prelude
:also <filenames> read additional modules
:reload             repeat last load command
:project <filename> use project file
:edit <filename>  edit file
:edit               edit last module
:module <module>  set module for evaluating expressions
<expr>            evaluate expression
:type <expr>      print type of expression
:?                  display this list of commands
:set <options>    set command line options
:set                help on command line options
:names [pat]        list names currently in scope
:info <names>     describe named objects
:browse <modules> browse names defined in <modules>
:find <name>      edit module containing definition of name
:!command           shell escape
:cd dir             change directory
:gc                 force garbage collection
:version            print Hugs version
:quit               exit Hugs interpreter

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Defining Functions and Constants

A Haskell (Hugs) program is stored in one or more files called scripts. Scripts with a .lhs extension are called literate scripts. In a literate script all lines are assumed to be comments unless they are preceeded by the '>' symbol.
  
The basic syntax for declaring a constant is:

   const = exp
   
Here are a few examples:

> pie = 3.1416
> val = 6 * 7

The basic syntax for defining a function is:

   fun param param ... = exp
   
Here are a few examples of function definitions:

> square x = x * x
> area r = pie * square(r)

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Haskell (Hugs) types include:

   Int, Float, Char, Bool, String
  
If A and B are types, then so are:

   A->B   maps from A to B
   (A, B) tuples of A and B
   [A]    lists of A
   
There are two types of type declarations:

   type name = tp
   data name = Constructor tp1 ... tpn | ...
   
Here are a few examples:

> type Temperature = Float
> type Vec3D = (Float, Float, Float)
> data Seasons = Fall | Spring | Summer | Winter

We can declare the types of the functions and constants we declare using the syntax:

   name:: Type
   
Here are a few examples:

> answer:: Bool
> answer = True

> origin:: Vec3D
> origin = (0, 0, 0)

> cube:: Float -> Float
> cube x = x * x * x
   
This is optional, because Haskell will infer the
type, anyway.

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> double x = x + x